I used to boil across 2 burners of the kitchen stove. No problem only getting boiling on the ends, water heat transfer is very fast. The water will be plenty hot in between burners for conversion. Even after the burners are shut off the water is hot enough for conversion. I don't know the lower threshold temp at which conversion happens, but it's got some tolerance, I'm guessing conversion will happen with water down to 190 ish.